Microscopic Stowaways on the ISS

Fungi come in a wide variety of sizes and forms. Tiny, one-celled
yeasts
(inset) are important for baking breads and fermenting wines,
beers and vinegars. Many medicines are produced with the help
of fungi, most notably, the antibiotic, Penicillin. Mushrooms
are fungi we buy at the supermarket.

Once on the Space Station, the air, water and surfaces with which the crew members interact
must be kept clean.

The air in the Space Station will be kept in constant motion, and all the
air on the Station will pass through filters -- called High Efficiency
Particle Air (HEPA) filters -- on its way to the temperature and
humidity control systems.

"The filters were originally designed to remove particulates," Pierson said.
"They're very good at removing small particles," such as microbes.

Microbes can ride in the air on particles of dust or in tiny clumps of bacteria
or fungi. On Earth, there might be a couple hundred or thousand
microbes in each cubic meter of air.

Water will be disinfected by a machine called a "catalytic oxidator," which
heats the water to as much as 265 degrees F. The organic molecules
in microbes are oxidized by this process, which kills nearly all
of them. Just to be sure, the water is then treated with iodine.

After this disinfection, the water should have less than 100 microbes in
100 milliliters of water.

"The water is extremely clean if you compare it to the water that you drink
at home," Roman said. "The water on the Station is many, many
times cleaner."

For the health of the crew as well as the Station's hardware, microbes must also
be kept from growing on surfaces and in nooks and crannies.

"The biggest threat to the Station from the microbes is degradation of the
materials," Roman said. "They'll eat pretty much anything."

"As they grow on surfaces, (fungi) produce an acid which will eventually corrode
the material," Roman continued. "They start using most materials
as a source of food. Have you seen bathroom tile that's been overgrown
by mold? Over time, you will notice that the mold has kind of eaten
the tile and grout."